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Engine issues

Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by BoneHead, Sep 25, 2012.

  1. BoneHead

    BoneHead Member

    Hey guys. I know I haven't posted anything here in a while, but I've been busy and I need some ideas for things to look at on my 'burban. This was the first place I thought of to ask. First off, it's a 98 1500 4x4, 5.7, mostly stock. Had the truck since January of this year. Ran like crap, but it's running almost new now. Although there are still a few issues I can't figure out.

    Here's what has been done so far...

    New Magnaflow cats (dual exhaust)
    Used Flowmaster mufflers
    3 new O2 sensors, 4th one wasn't throwing a code (it's the one after the cat on driver side)
    New plugs, wires, cap, etc
    New thermostat (3 times)
    New temp sensors (one in thermostat housing, one in block on driver side)
    New fuel injectors (the upgrade mpfi setup)
    New air filter
    A couple oil changes (just because I drive it every day)
    Cleaned plenum and upper intake when I changed injectors
    Cleaned MAF sensor with that MAF sensor spray stuff (can't think of the name right now)
    New PCV valve

    I think that's it. If I think of anything I'll put it in a new post.

    Here's the issue...
    When I first start it, the engine wants to hesitate a little. After about 2 or 3 minutes it clears up. Doesn't matter if the engine is cold or warmed up. If I turn it off, it does it again upon startup. Could have only been sitting 5 minutes and it'll do it. After it clears, she runs like a champ. Still throwing lean codes on bank 2, the reason I changed out both O2 sensors on that side. I inspected the wires and from what I can see of them they look fine. Even took a look a some vacuum lines and the few that I found looked good.
    Second issue, going by the gauge, when it's warming up, the temp goes up to about 255 deg before the thermostat opens. After that, it goes back down to 210, then up to 220 and stays. 3 different thermostats did the same thing. I replaced the temp sensors because one of them was not working properly. Gauge would never get past 125 deg. Some of the research I did said this may be causing the lean issue, but it's still doing it. Thinking one of those may be an out of box failure, but I'm not sure.

    Sorry for the long post, but as you can tell, I've got a couple issues and running out of things to check. Any help would be greatly appreciated.
  2. Pikey

    Pikey Moderator Staff Member 2 Years ROTM Winner 1000 Posts

    are you using the fail safe thermostats? running that cool could cause it to run funny. [MENTION=12002]moogvo[/MENTION] can explain what the computer does when it is running cold better than I can. I did not see fuel filter change on your list
  3. BoneHead

    BoneHead Member

    Yes they are fail safe thermostats. Supposed to open at 195 deg. I'm ok with it running at around 220, just wondering why the hell it's going up to 255 before it opens up. I was thinking at one point that maybe my dumb butt put it in upside down, but that wasn't the case. I know it's in there right.

    Yea, there was a new fuel filter done. Thought I put it on there.

    btw, Thanks for the relply Pikey
  4. Pikey

    Pikey Moderator Staff Member 2 Years ROTM Winner 1000 Posts

    I have NEVER had luck with the fail safe. Every time I have used them They have done exactly what yours are doing. They got warm, opened up and then stayed open never letting the vehicle get back to correct operating temp. I would try putting a regular thermostat in and see if that solves the temp issue. That might help with some of the running issues also.
    Last edited: Sep 26, 2012
  5. BoneHead

    BoneHead Member

    I'll do that. Hopefully the rain will hold off long enough for me this weekend. Although we desperately need it here. I pray I'm not putting a jinx on us saying that.

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